A Colin Forbes is where a person takes a sex move/position and completely makes up a definition for it that is nowhere close to the real definition. This can only happen if said person has absolutely no idea what they are talking about.

He Colin Forbes'd you yesterday when you asked him what a blumpkin was. According to Colin Forbes, a blumpkin is where you make a hole in a pumpkin and stick your dick inside of it and swing it around to jerk yourself off.